History of linguistics (19th century) ; History of linguistics (20th century) ; History of language ; Einfluss von Sprachen aufeinander; Sprachberührung; Areallinguistik; Languages in contact ; Adstratum language; Adstratsprache; Neighbor languages ; Comparative linguistics; Komparatistik; Indogermanistik; Indoeuropäische Sprachwissenschaft; Indoeuropean linguistics; Proto-Indo-European; Historical comparative linguistics ; Altkirchenslawisch; Old Church Slavonic; Neukirchenslawisch; New Church Slavonic; Church Slavonic ; Mitteltschechisch; Middle Czech; Old Czech